The present invention relates to a process for the production of vinyl acetate monomer according to the preamble of claims 1 and 15.
The invention relates to improved integrated methods of making vinyl acetate monomers from ethane or ethylene using metal oxide catalysts.
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains.
The utilization of lower alkanes (C1-C4) as feed stock to produce value added petrochemicals is an industrially desired process. Lower alkanes are low cost and environmentally acceptable because of their low chemical reactivity. There are only a few commercially available chemical catalytic processes, which utilize lower alkanes as a feed, such as butane to maleic anhydride.
Vinyl acetate monomer (VAM) is a well-known industrial chemical. The production of VAM from ethylene, oxygen and acetic acid using conventional VAM catalysts is known in the art. VAM is typically used as a raw material for vinyl resins such as polyvinyl acetate. VAM was previously primarily manufactured from the vapor phase reaction of ethylene, acetic acid and oxygen with a zinc acetate catalyst.
More recently, VAM has been produced from the vapor-phase reaction of ethylene, acetic acid and oxygen, with a palladium catalyst. For example, VAM may be made from ethylene wherein the first step involves reacting the ethylene to form acetic acid, followed by a second step of reacting a mixture of the acetic acid and ethylene to form vinyl acetate.
Numerous methods are known for the catalytic oxidation of ethylene to acetic acid. See, for example, U.S. Pat. Nos. 3,792,087 and 3,970,697. Similarly, numerous methods are known for the catalytic production of vinyl acetate by reacting ethylene with acetic acid and oxygen in the gaseous phase. See, U.S. Pat. Nos. 3,190,912; 3,637,819; 3,650,896; 4,370,492; 5,185,308; and 4,902,823.
PCT Patent Publication WO 98/05620 describes the production of acetic acid and/or vinyl acetate from ethylene (or ethane) using a first catalyst active for the oxidation of ethylene to acetic acid and/or active for the oxidation of ethane to acetic acid, ethylene and carbon monoxide, and a second catalyst active for the production of vinyl acetate. The patent also describes an additional necessary step for conversion of carbon monoxide to carbon dioxide. This is because carbon monoxide is poisonous to the VAM catalyst.
U.S. Pat. No. 4,188,490 relates to a catalytic oxidation process for the production of mixtures of acetic acid and vinyl acetate comprising the step of contacting a feed mixture containing ethylene, oxygen and water (as steam) with a catalyst composition to provide a mixture of acetic acid and vinyl acetate. The catalyst system comprises a palladium metal on a zinc oxide support treated in the presence of a sulfur modifier. The method requires the subsequent step of fractional distillation to separate the acetic acid from the vinyl acetate. Alternatively, the acetic acid contained in the product mixture is converted in situ to an alkali metal salt such as sodium acetate. The method also requires the step of treating the catalyst with the sulfur modifier by, for example, flowing moist air containing SO2 over the catalyst at 200xc2x0 C. for about one hour.
WO 99/13980 discloses an oxide catalyst comprising the elements Mo, V and Nb with small amounts of phosphorus, boron, hafnium, Te and/or As. The modified catalyst provides both higher selectivity and yield of acetic acid in the low temperature oxidation of ethane with molecular oxygen-containing gas. A process for the higher selective production of acetic acid by the catalytic oxidation of ethane wish oxygen, in the presence of the improved catalyst.
WO 98/05620 describes acetic acid and/or vinyl acetate which are produced by an integrated process which comprises the steps: (a) contacting in a first reaction zone a gaseous feedstock comprising ethylene and/or ethane and optionally steam with a molecular oxygen-containing gas in the presence of a catalyst active for the oxidation of ethylene to acetic acid and/or ethane to acetic acid and ethylene to produce a first product stream comprising acetic acid, water and ethylene (either as unreacted ethylene and/or as co-produced ethylene) and optionally also ethane, carbon monoxide, carbon dioxide and/or nitrogen; (b) contacting in a second reaction the presence or absence of additional ethylene and/or acetic acid at least a portion of the first gaseous product stream comprising at least acetic acid and ethylene and optionally also one or more of water, ethane, carbon monoxide, carbon dioxide and/or nitrogen with a molecular oxygen-containing gas in the presence of a catalyst active for the production of vinyl acetate to produce a second product stream comprising vinyl acetate, water, acetic acid and optionally ethylene; (c) separating the product stream from step (b) by distillation into an overhead azeotrope fraction comprising vinyl acetate and water and a base fraction comprising acetic acid, (d) either (i) recovering acetic acid from the base fraction separated in step (c) and optionally recycling the azeotrope fraction separated in step (c) after partial or complete separation of the water therefrom to step (c) or (ii) recovering vinyl acetate from the azeotrope fraction separated in step (c) and optionally recycling the base fraction separated in step (c) to step (b), or (iii) recovering acetic acid from the base fraction separated in step (c) and recovering vinyl acetate from the overhead azeotrope fraction recovered in step (c).
DE-A-19630832 relates to a process for the selective preparation of acetic acid from a gaseous feed comprising ethane, ethylene or mixtures thereof plus oxygen at elevated temperature, which comprises bringing the gaseous feed into contact with a catalyst comprising the elements Mo, Pd, X and Y in gram atom ratios a:b:c:d in combination with oxygen where the symbols X and Y have the following meanings; X is one or more elements selected from the group consisting of: Cr, Mn, Nb, Ta, Ti, V, Te and/or W, in particular Nb, v and W; Y is one or more elements selected from the group consisting of: B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Cu, Rh, Ir, Au, Ag, Fe, Ru, Os, K, Rb, Co, Mg, Ca, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, TI and U, in particular Ca, Sb, Te, and Li. This invention further provides a catalyst for the selective preparation of acetic acid comprising the elements Mo, Pd, X and Y in the gram atom ratios a:b:c:d in combination with oxygen.
Several methods for producing vinyl acetate from ethylene result in the production of carbon monoxide. The production of carbon monoxide is disadvantageous because it is poisonous to the second stage catalyst. Moreover, carbon monoxide is also a less desirable by-product due to environmental law constraints. In order to avoid this problem, it is necessary to introduce another catalytic reactor for the total oxidation of CO to CO2. This can add significant costs to the catalytic process.
Accordingly, it would be desirable to provide an improved method for the selective production of vinyl acetate monomer from ethane without the production of carbon monoxide.
It is an object of the invention to overcome the above-identified deficiencies.
It is another object of the invention to provide an improved catalytic method for the production of vinyl acetate.
It is a further object of the invention to provide an improved catalytic method for the oxidation of ethylene to produce vinyl acetate.
It is a further object of the invention to provide an improved catalytic method for the oxidation of ethane to produce vinyl acetate.
It is a still further object of the invention to provide an improved catalytic method for the oxidation of ethane, ethylene or a mixture of ethane and ethylene to produce vinyl acetate without the production of carbon monoxide as a by-product.
It is yet another object of the invention to provide an improved catalytic method for the single stage oxidation of ethane or ethylene or mixtures thereof to vinyl acetate.
The foregoing and other objects and advantages of the invention will be set forth in or be apparent from the following description.
The process of the present invention is defined in the characterizing portion of claims 1 and 15.
According to the present invention, vinyl acetate is produced catalytically from ethane feed stocks. Another aspect of the invention relates to the production of vinyl acetate from ethylene. The catalysts suitable for use in the methods of the invention are active and selective to the desired end product, vinyl acetate. The catalytic process for the production of VAM from ethane involves two steps. In the first step, a catalyst (the xe2x80x9cfirst catalystxe2x80x9d) is used to provide the function of activation of ethane to ethylene and acetic acid. In the second step, ethylene and acetic acid are further oxidized to VAM in the presence of a conventional VAM catalyst (the xe2x80x9csecond catalystxe2x80x9d). Another preferred embodiment relates to a method of forming a stoichiometric mixture of ethylene and acetic acid using the first catalyst, which mixture can be directly fed into a vinyl acetate reactor containing the VAM catalyst without adjustments. Yet another preferred embodiment relates to a catalytic method wherein ethylene or ethane is converted to vinyl acetate in a single stage reactor.
Advantageously, the preferred catalytic methods of the invention do not produce carbon monoxide. This is advantageous because carbon monoxide is not environmentally friendly and can have a significant impact on down stream separation costs, as well as on the poisoning of the VAM catalyst.